1. Field of the Invention
The present invention relates to a voltage controlled oscillator (VCO) applied to a phase-locked loop (PLL) of a communication terminal or a broadcasting receiver, and more particularly, to a VCO that can stably generate a clock of a 50% duty from a simple circuit and have an excellent duty correction function in noise.
2. Description of the Related Art
A VCO is an important element used in a tuner or a modem of a communication system or a broadcasting system. Since a system has been more complicated, required properties for the VCO become more diverse and strict. Especially, various kinds of systems require a clock of a 50% duty to process data accurately.
FIG. 1 is a view of a related art VCO.
The VCO includes a VCO unit 10 generating a signal S1 with a frequency according to a control voltage VC, and a flip-flop 20 generating a signal Sout with a 50% duty through performing a divide-by-2 on the output signal S1 of the VCO unit.
FIG. 2 is a timing chart of main signals in the VCO of FIG. 1.
Referring to FIG. 2, the signal S1 outputted from the VCO unit 10 has duty lower than 50%. The flip-flop 20 is required to make the signal S1 to be a 50% duty. Then the flip-flop 20 outputs a signal having a 50% duty. Here, the signal Sout outputted from the flip-flop 20 corresponds to a frequency (Fvco/2) that is a half frequency Fvco in the VCO unit 10.
However, the related art VCO needs to generate a frequency outputted from the VCO unit, which is two times higher than a frequency of a final output.